Real-time applications require a set of transport services not
currently provided by widely-deployed transport protocols. Ossification
prevents the deployment of novel protocols, restricting solutions to
protocols using either TCP or UDP as a substrate. We describe the
transport services required by real-time applications. We show that, in
the short-term (i.e., while UDP is blocked at current levels), TCP
offers a feasible substrate for providing these services. Over the
longer term, protocols using UDP may reduce the number of networks
blocking UDP, enabling a shift towards its use as a demultiplexing
layer for novel transport protocols.